Classification and characteristics of sedimentary rocks. Sedimentary rocks

1) clastic rocks - products of predominantly physical weathering of parent rocks and minerals with subsequent transfer of material and its deposition in other areas;

2) colloidal-sedimentary rocks - the result of predominantly chemical decomposition with the transition of a substance into a colloidal state (colloidal solutions); this also includes the finest classes of clastic rocks and residual rocks of the weathering crust;

3) chemogenic rocks - sediments that fall out of aqueous, mainly true, solutions - the waters of seas, oceans, lakes and other basins by chemical means, i.e. as a result of chemical reactions or supersaturation of solutions caused by various reasons;

4) biochemical rocks, including rocks formed during chemical reactions with the participation of microorganisms, and rocks that can have two origins: chemical and biogenic;

5) organogenic rocks formed with the participation of living organisms; In part, these rocks are direct products of the vital activity of organisms and always contain a significant amount of remains of dead animals and plants, or are entirely constructed from substances of organic origin.

Under sedimentary rock structure refers to the structure of rocks, determined by the shape, size and relationship of the components that make up the rock. The classification of sedimentary rock structures is based on a genetic basis, therefore clastic, chemogenic and biogenic structures are distinguished. Therefore, we will consider the structures of sedimentary rocks when studying these three genetic types.

Sedimentary rock texture - a feature of the spatial arrangement of rock components. There are two main types of textures - in-situ and surface. Let's look at some textures characteristic of sedimentary rocks. As individual sedimentary rocks are described, other textures will also be considered. Sedimentary rocks contain both massive and porous textures.

Sedimentary rocks are formed as a result of the process of sedimentation on the earth's surface. The source material of sedimentary rocks are the products of the destruction of previously formed rocks, the vital activity of organisms and some chemical compounds. The most common types of sedimentary rocks include sandstones, limestones, and clays. Their classification is based on the chemical composition and size of the constituent particles. Minerals most commonly found in these rocks , - quartz, calcite and gypsum. The finest-grained varieties of sedimentary rocks are called clayey or mudstone, medium-grained varieties are called sandy; the coarsest-grained varieties are coarse-grained or ruditic. Sedimentary rocks occur in the form of layers or strata.

10. The concept of soil. Classification of soils according to GOST 25100-95.

Priming - any rocks, soils, sediments, technogenic (anthropogenic) formations, which are multicomponent, dynamic systems that are components of the geological environment and the object of human engineering and economic activity.

Classification

· Class of natural rocky soils - soils with rigid structural bonds (crystallization and cementation) are divided into groups, subgroups, types, types and varieties according to Table 1.

· Class of natural dispersed soils - soils with water-colloidal and mechanical structural bonds are divided into groups, subgroups, types, types and varieties according to Table 2.

· Class of natural frozen soils* - soils with cryogenic structural connections are divided into groups, subgroups, types, types and varieties according to Table 3.

· Class of technogenic (rocky, dispersed and frozen) soils - soils with various structural connections formed as a result of human activity, are divided into groups, subgroups, types and types according to Table 4.

· Particular classifications by material composition, properties and structure of rocky, dispersed and frozen soils (varieties) are presented in Appendix B.

11. Clastic rocks, their names, the size and shape of the particles composing them, the nature of the bonds between grains. The main engineering-geological features of clastic rocks.

Clastic rocks -clastic rocks, sedimentary rocks, consisting entirely or predominantly of fragments of various rocks (igneous, metamorphic or sedimentary) and minerals (quartz, feldspars, micas, sometimes glauconite, volcanic glass, etc.).

There are O. g. p. cemented and uncemented, loose. In cemented O. g. p. binders are carbonates (calcite, dolomite), silicon oxides (opal, chalcedony, quartz), iron oxides (limonite, goethite, etc.), clay minerals, and a number of others. O. g. p. . often contain organic remains: mollusk shells, etc., tree trunks and branches, etc.

The classification of O. g.p. is based on a structural feature - the size of the fragments. Coarse clastic rocks with a fragment size of more than 1 mm(uncemented - blocks, boulders, pebbles, crushed stone, gruss, gravel; cemented - Conglomerates, Gravelites, etc.); sandy rocks, or psammites, with a particle size of 1-0.05 mm(sands and sandstones); silty rocks, or silts, with a particle size of 0.05-0.005 mm(silts and siltstones); clayey rocks, or Pelites, with a particle size of less than 0.005 mm(clays, mudstones, etc.). Sometimes the boundary between silts and pelites is drawn by particle size 0.001 mm. Clay rocks can be of either chemical or clastic origin. O. g.p. of mixed composition are also distinguished, composed of fragments of various sizes - sandy, silty and clayey. These include the widespread, especially among modern continental deposits, various loams and sandy loams. Further subdivision of O. g.p. within structural subtypes is made according to the mineral composition of the fragments and other characteristics. Products also belong to O. g.p. volcanic eruptions: volcanic rubble, ash - loose rocks and their cemented varieties - tuffs, tuff breccias and transitional rocks between clastic and volcanogenic - tuffites and tuffogenic rocks.

With dissected relief and high environmental dynamics, coarse rocks are formed; in conditions of flat terrain and low speeds of water and air flows, sand, silt and clay rocks are formed. Clay particles settle mainly in calm water. In the coastal part of the seas and oceans, pebbles and gravel are deposited on the beach and shallow waters; as they move deeper into the basin, they are replaced by sands, silts and, finally, clayey silts at a depth below the level of action of waves and currents. However, there are pebbles and sands at great depths - the result of the action of various bottom currents and turbidity currents.

O. g.p. is used as a building material, sands are used in the glass and metallurgical industries. In river and sea sands there are placers of gold, platinum, precious stones, minerals of titanium, tin, tungsten, rare and radioactive elements.

12. Sedimentary mountain chemogenic and organogenic: classification by origin, features of composition, structure, texture. The most important engineering-geological features of chemogenic and organogenic rocks.

ORGANOGENIC ROCKS – sedimentary rocks consisting of the remains of animals and plants and their metabolic products. Organisms have the ability to concentrate certain substances that do not reach saturation in natural waters, forming skeletons or tissues that are preserved in a fossil state.

According to the material composition, among organogenic rocks one can distinguish carbonate, siliceous, and some phosphate rocks, as well as oil shale, oil, and hard bitumen. Organogenic carbonate rocks (Limestones) consist of shells of foraminifera, corals, bryozoans, brachiopods, mollusks, algae and other organisms.

Their peculiar representatives are reef limestones that make up atolls, barrier reefs and others, as well as writing chalk. Organogenic siliceous rocks include: diatomite, spongolite, radiolarite, etc. Diatomites consist of opal skeletons of diatoms, as well as spicules of siliceous sponges and radiolarians. Spongolites are rocks that usually contain more than 50% spicules of flint sponges. Their cement is siliceous, made of opal rounded bodies, or clayey, slightly calcareous, often including secondary chalcedony. Radiolarites are siliceous rocks, more than 50% consisting of radiolarian skeletons, which form radiolarian silt in modern oceans. In addition to radiolarians, they include sponge spicules, rare diatom shells, coccolithophores, opal and clay particles. Many jaspers have a radiolarian base.

According to the conditions of formation (mainly in relation to carbonate rocks), one can distinguish between bioherms - an accumulation of the remains of organisms in a lifetime position, thanato- and taphrocenoses - the joint burial of dead organisms that lived here or were transported by waves and currents; rocks that arise from planktonic organisms are called planktonic (for example, diatomite, chalk, foraminiferal limestone).

If organic remains are crushed as a result of the action of waves and surf, organogenic-clastic rocks are formed, consisting of fragments (detritus) of shells and skeletons, held together by some mineral substance (for example, calcite).

CHEMOGENIC ROCKS - a group of rocks formed directly by chemical precipitation from water or solutions without the participation of biological processes.

Depending on the method and place of deposition, as well as the origin of waters and solutions, chemogenic rocks can be sedimentary, hydrothermal-sedimentary, and hydrothermal. Precipitation methods: gradual concentration of waters and solutions as a result of solar evaporation, mixing solutions of 2 or more soluble salts and lowering the temperature of the solutions. By origin, mineral-forming waters and solutions can be marine or continental hydrothermal (weakly mineralized and brine).

Place of deposition; surface (sea and continental bodies of water) or interior of the Earth. In the first case, extended sheet bodies are formed, in the second - fissure-vein lens-shaped bodies.

The predominant part of chemogenic rocks is hybrid - hydrothermal-sedimentary, to a lesser extent - sedimentary and hydrothermal.

The composition of mineral-forming waters and solutions, as well as tectonic and climatic conditions determine the mineralogical composition of chemogenic rocks and the value of their use as a mineral.

Chemogenic rocks include all mineral salts, potassium salts, evaporites, soda, flints and flints in association with tripoli, phosphorites, ferromanganese ores, bauxites, chemogenic limestones, travertines, most of lead-zinc, sulfur, boron and lithium ores, which are valuable raw materials for the development of various industries.

13. Metamorphic rocks, their origin, occurrence patterns, mineral composition, structure, texture and properties in the sample and massif.

Metamorph And chesical g O pores O yes -rocks that were previously formed as sedimentary or igneous, but have undergone changes (metamorphism) in the interior of the Earth under the influence of deep fluids, temperature and pressure, or near the earth’s surface under the influence of the heat of intrusive masses.

The most common metamorphic rocks have a schistose or banded texture - schists, gneisses, although massive rocks, such as marbles, quartzites, and hornfels, are also common. In addition, rocks with cataclastic textures that arose during dislocation or dynamic metamorphism are widely developed - various cataclasites and mylonites.

The composition of metamorphic rocks, as well as their physical and mechanical properties, varies widely. There are metapelites - derivatives of acidic sedimentary and igneous rocks (argillites, siltstones, sandstones, granitoid volcanics and intrusive rocks) and metabasites - derivatives of basic sedimentary and igneous rocks. Carbonate metamorphic rocks - marbles, calciphyres, carbonate cataclasites - stand apart.

Based on the nature of the temperature effect, a distinction is made between regionally metamorphosed (low temperature gradient, huge regional volumes of metamorphic rocks that arose in similar temperature and pressure ranges) and contact-metamorphosed rocks (locally high temperature gradients near igneous bodies, shallow depths, small volumes of metamorphic rocks). rocks formed in similar temperature and pressure ranges, concentric zoning near intrusive bodies). Contact-metamorphosed rocks formed from clayey and other aluminosilicate rocks are hornfels, from limestones - marbles, bauxites - emery.

Among the regionally metamorphosed rocks there are Various types metamorphic rocks characteristic of certain facies of metamorphism. These are a variety of shales from low-temperature chlorite and sericite to crystalline schists of various compositions formed under high-temperature conditions. Metabasites with essentially hornblende-plagioclase composition are called amphibolites. Gneisses are metapelitic banded rocks of high stages of metamorphism, close to granitoids in chemical composition. Many researchers classify eclogites as high-pressure metamorphic rocks (1500 MPa), massive essentially garnet-pyroxene rocks with a significant content of pyrope in garnet and jadeite in pyroxene.

14. Absolute and relative age of rocks. Method for determining the age of rocks. Geological time scale.

Geological age– age of rocks. Geological age is the time that has passed since a certain event in the geological history of the Earth: the deposition of a layer of rocks, the formation of mountains, glaciation, etc. A distinction is made between relative and absolute geological age.

· Absolute geological age – the age of rocks expressed in absolute units of time; is established based on the study of the decay of radioactive elements (uranium, thorium, potassium, rubidium, etc.) contained in minerals. It is usually estimated in million years. The term is used conditionally, since each of the obtained figures is not “absolute” and is often given as a first approximation (with a minimum error of ± 5%).

· Relative geological age – the age of rocks, established on the basis of the relative position of the layers in the section. When the layers are gently bedding, the lower ones are more ancient, and the upper ones are younger (the law of bedding sequence). Comparison of sedimentary strata of areas remote from each other made it possible to create a general stratigraphic scale, divided into a number of segments (systems) characterized by a specific complex of plant and animal remains. By analyzing the fossils found in the strata, the sediments are linked to a general scale, i.e., the relative geological age is determined.

· tratigraphic method is based on the fact that the age of a layer under normal occurrence is determined - the underlying layers are more ancient, and the overlying layers are younger. This method can also be used for folded layers. Cannot be used on overturned folds.

· Lithological method is based on the study and comparison of the composition of rocks in different outcrops (natural - on the slopes of rivers, lakes, seas, artificial - quarries, pits, etc.). In a limited area, sediments of the same material composition (i.e., consist of the same minerals and rocks) can be of the same age. When comparing sections of different outcrops, marking horizons are used, which are clearly distinguished from other rocks and are stratigraphically consistent over a large area.

· Tectonic method is based on the fact that powerful processes of rock deformation occur (as a rule) simultaneously over large areas, therefore strata of the same age have approximately the same degree of dislocation (displacement). In the history of the Earth, sedimentation periodically gave way to folding and mountain building.

· Biostratigraphic or paleontological methods consist in determining the age of rocks through the study of fossil organisms.

· Determining the relative age of igneous and metamorphic rocks (all of the methods described above are used to determine the age of sedimentary rocks) is complicated by the lack of paleontological remains. The age of effusive rocks occurring together with sedimentary rocks is determined by their relationship to sedimentary rocks.

· The relative age of intrusive rocks is determined by the relationship between igneous rocks and host sedimentary rocks whose age has been established.

· Determining the relative age of metatharmophic rocks is similar to determining the relative age of igneous rocks.

15. Geological maps and sections.

Geological map is an image of the geological structure of a certain area of ​​the earth's crust. It gives an idea not only of the geological structure of the earth’s surface, but to a certain extent also of internal structure earth's crust.

There are three types of engineering-geological maps: 1) engineering-geological conditions, 2) engineering-geological zoning and 3) engineering-geological maps for special purposes. Each such map includes symbols (Fig. 91), geological sections and an explanatory note. The map of engineering-geological conditions contains information for all types of ground construction.

The map of engineering-geological zoning reflects the division of the territory into parts (regions, regions-districts, etc.) depending on the generality of their engineering-geological conditions.

Special purpose maps are drawn up in relation to specific types of construction. They contain an assessment of the engineering-geological conditions of the construction site and a forecast of engineering-geological phenomena.

The basis for compiling a geological map is the following. principles: on the map conventional signs(color-paint, shading, letter indices and other signs) shows the distribution of sedimentary, igneous and metamorphic rocks of various ages. The composition and age of rocks is indicated by color and special symbols. Lines of different thicknesses indicate the geological boundaries of rocks that make up geological bodies and tectonic disturbances - faults. The shape of the boundaries allows us to judge the conditions of occurrence, the relationship of rocks, geological structures and the behavior of rocks at certain depths.

Geological sections represent a projection of geological structures onto a vertical plane and make it possible to identify the geological structure in depth. They are built according to a geological map or according to data from exploration workings (pits, boreholes). The vertical scale of sections is usually taken to be 10 or more times larger than the horizontal one.

The geological section shows the age, composition, thickness, soil conditions, and hydrogeological conditions.

16. Tectonic movements of the earth's crust. Folds, cracks and breaks in the earth's crust.

Tectonic movements and their significance in the formation of crystalline basement.

Processes of internal dynamics (endogenous processes) can be divided into:

1 – magmatism;

2 – metamorphism (high pressure and temperature);

3 – tectonic.

They are all closely related to each other and mutually influence.

Movements of the earth's crust with its deformations and changes in the occurrence of rocks are called tectonic processes. They can be divided into three main types:

Oscillatory - slow rise and fall of sections of the earth's crust with the formation of large bulges and deflections;

Folded - the collapse of horizontal layers of the earth's crust into folds without breaking them;

Fracture - with rupture of layers and rock masses.

Oscillatory movements. Certain sections of the earth's crust rise over many centuries, while others fall at the same time, changing on the contrary over time. There are types of such movements of the earth's crust: 1 - past geological periods; 2 – the latest of the Quaternary period; 3 – modern with changes in the heights of the earth’s surface in the area.

The crystalline foundation of the platform is uneven. The depressions in it are synclines, the rises are anticlines. The amplitude of vibrations on the platform reaches 2-3 km.

17. Seismic phenomena: earthquakes and tsunamis. Magnitude and magnitude of the earthquake.

Earthquake , geol., noticeable vibrations of the earth's crust occurring from the action of internal forces. There are slow, barely noticeable vibrations and rapid destructive movements of the layers of the earth's crust. The latter are known underground in a narrow sense, the causes of earthquakes: displacement, subsidence of layers of the earth's crust, failures due to erosion and, in general, the action of water and volcanic phenomena. The latter are accompanied by the release of water vapor, gases, slag, and dirt. To study the Earth, special stations (seismic) were set up with instruments (seismometers) that measure the speed of propagation of vibrations in the earth's crust.

Causes: There are two main causes of earthquakes:
One of them is surface processes that cause minor earthquakes. These processes involve plates drifting along great faults, such as the San Andreas Fault in California or the Alpine Fault in New Zealand, acting like scissors, crushing each other's edges.

The second reason reflects deeper processes occurring in zones along the edges of shifting plates, where the edges of these masses of the earth's crust plunge into the earth's mantle and, at a depth of about 500 km, are reabsorbed and absorbed. For this reason, larger earthquakes are already occurring.

EARTHQUAKE SIGNALITY - intensity of the earthquake, expressed in points. In the USSR, since 1952, the 12-point scale of S.V. Medvedev has been adopted. When determining B. z. this scale takes into account a combination of many signs: readings from seismological stations, the nature of damage to buildings and structures (with separate consideration of the types of buildings, the degree of damage and the number of damaged buildings), residual phenomena in soils and changes in the regime of ground and ground waters, subjective sensations of shocks and vibrations A simplified description of earthquakes of different magnitudes: 1-4 - weak, do not cause destruction; 5-7 - strong, destroy dilapidated buildings; 8 - destructive, factory chimneys fall, strong buildings are partially destroyed; cracks on the surface of the Earth; 10 - destructive, bridges are destroyed, pipelines are broken, landslides occur; 11 - disasters, destruction of all structures, changes in the landscape; 12 - severe disasters, large changes in the terrain over a vast area.

Magnet at yes earthquake e nia - a conventional value characterizing the total energy of elastic vibrations caused by earthquakes or explosions; is proportional to the logarithm of the vibration energy. Usually determined by the maximum ratio of the amplitude to the period of oscillations recorded by seismographs. M. z. allows you to compare vibration sources by their energy. Increase in M. z. per unit corresponds to a 100-fold increase in vibration energy. The strongest known earthquakes have M. z. no more than 9 (approximately corresponds to 1019 j or 1026 ergs). The strength of an earthquake is measured in points by shaking and destruction on the earth's surface and depends, in addition to the magnitude of the earthquake, on the depth of the source and the geological conditions of the epicentral zone. With a shallow focus, destruction can begin at the epicenter at M. z about 5, and with a focus at a depth of hundreds km at MZ equal to 7, almost no destruction occurs.

Tsunami -ocean waves long length(up to 1500 km), resulting from the upward or downward displacement of extended sections of the bottom during strong underwater and coastal earthquakes and, less commonly, due to volcanic eruptions and other tectonic processes. The period is from 15 to 60 minutes, the speed is from 50 to 1000 km/h, the height in the area of ​​occurrence is from 0.01 to 5 m, and near the coast 10 m or more (sometimes up to 50 m). Can lead to catastrophic consequences.

18. Seismic zoning and microzoning.

Seismic zoning - assessment of potential seismic hazard in a seismically active area. The identification of seismically hazardous areas is based on the results of a joint analysis of instrumental and macroseismic data on earthquakes of past years (intensity of vibrations on the Earth's surface, spatial distribution of earthquake sources, their sizes, magnitude and energy of earthquakes, frequency of occurrence, etc.) and geological features of the area (history of geological development, intensity and contrast of the latest and modern tectonic movements, age and nature of tectonic disturbances, their activity, etc.).

Clarification of the magnitude of seismic impacts on structures depending on the local conditions of a specific area of ​​the territory of a seismically hazardous area (physical and dynamic properties of soils and underlying rocks, thickness of the upper layers of the earth’s crust, the presence of permafrost rocks, tectonic conditions, relief features, spectral properties of incoming seismic waves, etc. . n.) is the subject of seismic microzoning. Graphic expression S. r. are maps containing information about the intensity of shaking (in points) for any geographical location under average ground conditions. According to the Building Codes and Regulations, average soil conditions include clays, loams, sands, sandy loams with a groundwater level deeper than 8 m from the Earth's surface, as well as coarse soils when the groundwater level is from 6 to 10 m from the Earth's surface. In the USSR, the total area of ​​earthquake-prone areas is 28.6% of the country's territory (including 9-point areas accounting for 2.4%, 8-point areas - 3.2%). areas of possible magnitude 9 earthquakes are located in Central Asia, Baikal region, Kamchatka, Kuril Islands, etc.; 8-point areas - in Moldova, Crimea, the Caucasus, Southern Siberia, etc.

Seismic microzoning is carried out with the aim of clarifying the characteristics of seismic hazard based on data from engineering and seismological studies on the foci of earthquakes with epicenters located at a distance of up to 100 km from the construction site, on the seismic regime of construction sites, on the seismic properties of the studied soil thickness, on the geomorphological conditions of the construction site and the influence of buried discontinuous tectonic structures under seismic influence.

The main geological task is to conduct field seismic studies to quantify relative changes (increment) in seismic intensity.

Seismic microzoning includes the following types works :

· study of materials from previously completed studies on engineering geology, seismotectonics and seismicity of the region, as well as data from general engineering geological surveys and aerospace sounding of the construction site;

· visual seismotectonic and macroseismic surveys at the construction site and adjacent territory;

· geological, geodetic, geophysical and geochemical works;

· comprehensive analysis the entire set of data obtained, compiled in the form of a summary report, including a map (scheme) of seismic microzoning of the construction site.

As a result of the work on seismic microzoning, the coefficients for the ground vibration parameters (acceleration, speed, displacement) corresponding to the initial seismicity of the construction area are determined. These coefficients take into account the seismotectonic situation in the construction area (Ks.t), seismic regime (Ks.r), local engineering and geological conditions (Kgr) and terrain (Kr.m).

19. The relief of the Earth's surface and its connection with tectonic movements.

The surface height within the continents varies from several tens of meters above sea level to several kilometers - the snowy peaks of the Himalayas stretching far into the sky. The most characteristic feature of the surface structure is the sharp junction of areas of different heights. Oceans and continents. Mountain systems - the Himalayas, Cordillera, Alps, Caucasus, Tien Shan and others - rise in clearly isolated blocks above the surrounding plateaus or lowlands. Plateaus and lowlands are no less sharply demarcated from each other, for example, the desert areas of Eastern Australia with altitudes up to 1500 m and the lowland adjacent to it from the east with elevations rarely exceeding 100 m, bordering along a line running almost across the entire continent in the northeast direction.

The combination of areas of different heights is such a striking feature that if you look at physical card world, then the continents will appear in the form of a mosaic, consisting of areas of various shapes and sizes, various shades green and brown. Globally, the largest units stand out, such as the Himalayas, Cordilleras, the Urals, Tien Shan, and the West Siberian Lowland. Each of these units, in turn, consists of separate sections of different heights - individual ridges, intermountain depressions, plateaus, etc.

And so, relief. This word comes from the French relief - bulge. It very accurately reflects the content embedded in it. In fact, despite the many different types of surface relief, its main, defining feature will be the general hypsometric level (i.e. absolute height, height above sea level) of the region as a whole and the relative difference in the heights of its individual sections. The shape and size of these areas, the nature of their transition, in other words, one or another combination of them are also important.

The first scientific hypothesis interpreting the formation of relief as interconnected with the development of the earth's crust was contraction. Based on the premises of this hypothesis, the hardened earth's crust underwent various mechanical dislocations due to a decrease in the volume of the planet's interior as it cooled. Folds (mountains), breaks, etc. appeared.

The hypothesis of plate tectonics is currently popular worldwide. According to this hypothesis, the movement of continents and individual plates of the earth's crust leads to the accumulation of masses of the earth's crust in certain zones - in the marginal parts of the plates or at their junction. For example, the emergence of the Himalayas is interpreted as a result of the rapprochement of Asia and the Hindustan Peninsula.

The surface relief that we observe was formed over an extremely long time. At the same time, it is obliged to the interaction of two differently directed forces: internal - endogenous and external - exogenous. The first are realized through tectonic processes, leading, whatever their nature, to the emergence of primary contrasting surface forms. Endogenous relief formation can be equally characterized by uplifts and subsidences.

Exogenous forces are aimed at smoothing out the contrasting shapes of the surface of the hill under the influence of atmospheric processes and water flows are destroyed, the depressions are filled with demolished material. Exogenous forces act continuously both during the formation of tectonic relief and later. Exogenous factors begin to prevail over endogenous ones only when tectonic processes become less active or completely die out.

So, the mosaic of the planet’s surface at different altitudes is due to the forms of tectonic relief.

20. Types of water in rocks (soils) and their influence on the condition and properties of rocks.

Groundwater is divided: according to the nature of its use - domestic and drinking water, technical, industrial, mineral, thermal; according to the conditions of occurrence in the earth's crust

21. The concept of groundwater. Origin of groundwater.

Groundwater is formed mainly by infiltration. Atmospheric precipitation, river and other waters, due to gravity, seep through large pores and cracks in rocks. At depth, they linger on the aquitard, and underground water horizons appear. The amount of water depends on many factors: the nature of the relief, the composition and permeability of soils, climate, vegetation cover, and human activity.

The waters of the earth's crust are constantly replenished with juvenile waters that arose in the depths of the earth with access to the surface of the Earth in the form of vapors and hot springs during volcanic activity. In zones of slow water exchange, mineralized (salty) waters of so-called sedimentary origin are formed from ancient marine sediments at the beginning of the geological history of the earth's crust.

. Groundwater is divided: according to the nature of its use - domestic and drinking water, technical, industrial, mineral, thermal; according to the conditions of occurrence in the earth's crust (Fig. 52) - high water, groundwater, interstratal, fissure, karst, permafrost. For engineering and geological purposes, groundwater is classified according to hydraulic characteristics - free-flow and pressure.

22. Physical and chemical properties of groundwater, their hardness, aggressiveness.

During hydrogeological studies, the following main physical properties of groundwater are determined: temperature, color, transparency, taste, smell and specific gravity.
The temperature of groundwater varies widely. In high mountain areas and in areas where permafrost is widespread, it is low; Highly mineralized waters in some places even have negative temperatures (-5° C and below). In areas of young volcanic activity, as well as in places where geysers emerge (Kamchatka, Iceland, etc.), the water temperature sometimes exceeds 100 ° C. The temperature of shallow groundwater. In mid-latitudes it usually varies between 5-12° C and is determined by local climatic (mainly) and hydrogeological conditions.

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Rocks are a natural collection of minerals of constant mineralogical composition, continuously forming an independent body in the earth's crust.

All of them are divided into 3 groups according to origin: igneous (intrusive and effusive), metamorphic and sedimentary. Metamorphic and igneous materials make up approximately 90% of the volume of the earth's crust, but they are not very common on the surface of the continents. The remaining 10% is occupied by sedimentary rocks (SRR), covering 75% of the earth's surface area.

Sedimentary rocks

This type of rock on the earth's surface, as well as near it, is formed under conditions of low pressure and temperature due to transformations of continental and marine sediments. Sedimentary rocks according to the method of formation are divided into 3 genetic groups:

• clastic(conglomerates, sands, silts, breccias) are coarse products formed as a result of mechanical destruction of parent rocks;
• clayey– dispersed products of chemical deep transformation of aluminosilicate and silicate minerals of parent rocks, which over time transformed into new mineral species;
• biochemogenic, organogenic and chemogenic breeds– products of precipitation from solutions, with the participation of various organisms, accumulations organic matter or waste products of various organisms.

Occupies an intermediate position between volcanic and sedimentary rocks whole group effusive-sedimentary rocks, and between the main groups of OGP there are transitions that occur when materials of different genesis are mixed. A characteristic feature of UGP associated with their formation is their layering, as well as their occurrence in the form of regular geometric layers.

Composition of sedimentary rocks

OGPs consist of components of different origin and mineral composition, which reflects the multiplicity of sources of sedimentation and the multistage nature of rock formation. A breed is a complex unity of heterogeneous components formed at different times. These include relict or detrital minerals, fragments of parent rock, various decomposition products of primary minerals, exogenous new formations that arose as a result of the precipitation of compounds from colloidal and true solutions, products of diagenesis, catagenesis and metagenesis.

The HGP includes chemogenic, terrigenous, cosmogenic, volcanogenic and biogenic material-genetic components, which are combined into two large groups: authigenic and allotigenic components.

Authigenic– arise locally in rock or sediments different stages changes, formation or destruction of rocks. They reflect the physical and chemical conditions of sedimentation. In sedimentary formations there are over 200 authigenic minerals: chlorites, salts, sulfates, glauconite, oxides and hydroxides of iron, aluminum, manganese, etc.; minerals of silica, iron, clays, phosphates, sulfides, carbonates and many others.

Allotigenic- these are components that include material brought from any other areas and placed in a sedimentation basin as a source of nutrition. This is mainly terrigenous or clastic material, as well as pyroclastic, cosmogenic or volcanic components. More than 240 allothigenic minerals and a huge number of fragments of various rocks are known.

Properties of basic sedimentary rocks

The main sedimentary rocks include: limestone and its varieties, sandstone and dolomite.

Limestone– mainly consists of calcium carbonate with an admixture of magnesium carbonate, clayey, ferruginous and other inclusions. The properties of limestone are varied and depend on their texture, structure and composition. They have high compressive strength (from 900 to 1500 kgf/cm2).

Sandstone– consists of mineral grains cemented by natural substances. Strength is in the range of 600-2600 kgf/cm 2, depending on the presence of impurities and cementing substance.

Dolomite– consists of the mineral dolomite, similar in properties to dense limestone.

Almost the entire periodic table is located in the bowels of the earth. Chemical elements form compounds among themselves that make up natural minerals. One or more minerals may be present in the rocks of the earth. In this article we will try to understand their diversity, properties and meaning.

What are rocks

This term was first used by our Russian scientist Severgin in 1978. The definition can be given as follows: rocks are a combination of several minerals of natural origin into a single whole, having a constant structure and composition. Rocks can be found everywhere, as they are an integral part of the earth's crust.

If you study the description of rocks, they all differ in the following characteristics:

• Density.
• Porosity.
• Color.
• Durability.
• Resistant to severe frosts.
• Decorative qualities.

Depending on the combination of qualities, they find application.

Variety of rocks

The division of rocks into different types is based on their chemical and mineral composition. The names of rocks are given depending on their origin. Let's consider what groups they are divided into. A generally accepted classification may look like this.

1. Sedimentary rocks:

• organogenic;
• chemogenic;
• mixed.

2. Igneous:

• volcanic;
• plutonic;
• hypabyssal.

3. Metamorphic:

• isochemical;
• metasomatic;
• ultrametamorphic.

Sedimentary rocks

Any rocks, when exposed to various factors, can become deformed and change their shape. They begin to collapse, the debris spreads, and can be deposited on the bottom of seas and oceans. As a result, sedimentary rocks are formed.

It is difficult to classify rocks of sedimentary origin, since most of them were formed under the influence of many processes, and therefore it is almost impossible to classify them into a specific group. Currently, this type of breed is divided into:

• Clastic rocks. Various examples can be given: the familiar gravel or crushed stone, sand and clay, and many others.
• Organogenic.
• Chemogenic.

Let's take a closer look at each type of breed.

Clastic rocks

They appear as a result of the formation of debris. If we classify them taking into account their structure, we distinguish:

• Cemented rocks.
• Uncemented.

The first variety has a connecting component, which can be represented by carbonates and clays. The second variety does not have such substances, therefore it has a loose structure.

It can also be clarified that clastic rocks often include traces and remains of plant and animal organisms. These include mollusk shells, preserved fossilized parts of stems, and insect wings.

The best known are clastic rocks. Examples confirm this. Clastic materials include the well-known sand and clay, crushed stone and gravel, as well as many others. All of them are widely used in the construction industry.

Chemogenic rocks

This group is a product of chemical reactions. These include salts, such as potash, and bauxite. The process of formation of this type of rock can go in two ways:

1. The gradual process of concentration of solutions. The influence of radiation from the sun cannot be excluded here.
2. The combination of several salts at low temperature.

The structure of such breeds will depend on the place of their appearance. Those that form on the surface of the earth have the shape of a layer, while the deep ones are completely different.

Rocks from this group are very widely used, examples only confirm this. Chemogenic breeds include:

• Mineral salts.
• Bauxite.
• Limestones.
• Dolomite and magnesite and many others.

In nature, quite often there are rocks in the formation of which various natural processes took part. The name of the rocks that originated in this way is mixed. For example, you can find sand mixed with clay.

Organogenic sedimentary rocks

If mountain rocks sometimes include the remains of living organisms, then this group consists only of them. It includes:

• Oil and shale.
• Bitumen.
• Phosphate rocks.
• Carbonate compounds, such as chalk used to write on a blackboard.
• Limestones.

If we talk about composition, limestone and chalk consist almost entirely of the remains of shells of ancient mollusks, foraminifera, corals, and also include algae. Considering that different organisms can give rise to an organogenic rock, they are divided into several varieties:

• Bioherms. This is the name given to clusters of living organisms.
• Thanatocenoses and taphrocenoses are the remains of organisms that lived in these places for a long time or were brought by water.
• Planktonogenic rocks are formed from organisms living in bodies of water.

Sediment grain size

This feature is one of the characteristics of the structure of sedimentary rocks. If you look at rocks, they can be divided into homogeneous and with inclusions. In the first option, the entire rock is perceived as a homogeneous mass, and in the second, individual fractions, grains and their shape and ratio can be considered.

If we consider the size of the fractions, we can distinguish several groups:

1. The grains are quite clearly visible.
2. Hidden granules visually appear structureless.
3. In the third group, it is impossible to examine the granularity without special equipment.

The shape of inclusions may be one of the criteria by which these rocks are divided. There are several types of structures:

• Hypodiomorphic. In this type, the grains are crystals obtained from a solution.
• The hypidioblastic type refers to an intermediate structure in which the redistribution of substances occurs in already hardened rock.
• Granoblastic, or leafy, has irregularly shaped crystals.
• The mechanoconforal type is formed as a result of the mechanical action of grains under the pressure of those layers that are located above.
• Non-conformal grain has the main feature in the form of different grain outlines, which leads to the appearance of voids and porosity.

In addition to structure, texture is also distinguished. The division is based on layering:

• Gradational. Its formation occurs at great depths under water.
• Interlayer occurs in some layers of water; this type includes clay lubricants and layers of sand in clay.
• Interlayering occurs when the layer thickness is large, a change can be observed color range layers. An example is the alternation of clay and sand.

There are many more classifications that can be given, but perhaps we’ll stop here.

Representatives of sedimentary rocks

We have already looked at sedimentary clastic rocks, we have also given examples of them, and now we will focus on others, which are also widespread in nature.

1. Gravelites. They are sedimentary rocks in the form of gravel. They consist of fragments of rocks and minerals of various sizes.
2. Sandy rocks. This includes sands and sandstones.
3. Silty rocks are somewhat reminiscent of sandstones, only they contain more stable minerals in the form of quartz and muscovite.
4. Siltstone is distinguished by the presence of roughness at the fracture, and the color depends on the cementing material.
5. Loams.
6. Clay rock.
7. Mudstones.
8. Marls are a mixture of carbonates and clay.
9. Limestones, which consist of calcite.
10. Dolomites resemble limestones, but instead of calcite they contain dolomite.

All these rocks are widely used in construction and other sectors of the national economy.

Metamorphic rocks

If we remember what metamorphosis is, it will become clear that metamorphic rocks appear as a result of the transformation of minerals and rocks under the influence of temperature, light, pressure, and water. The most famous of this group are: marble, quartzite, gneiss, slates and some others.

Since different types of rocks can undergo metamorphosis, the classification depends on this:

1. Metabasites are rocks that are obtained as a result of the transformation of igneous and sedimentary rocks.
2. Metapelites are the result of the transformation of acidic sedimentary rocks.
3. for example marble.

The shape of a metamorphic rock is preserved from its predecessor, for example, if the rock was previously arranged in layers, then the newly formed one will have the same shape. The chemical composition, of course, depends on the original rock, but under the influence of transformations it can change. The mineral composition can be different, and it can include either one mineral or several.

Igneous rocks

This group of rocks makes up almost 60% of the entire earth's crust. They arise as a result of the melting of rocks in the mantle or in the lower part of the earth's crust. Magma is a molten substance, partially or completely, enriched various gases. The formation process is always associated with high temperatures in the bowels of the earth. Geological processes occurring inside the earth constantly provoke magma to rise to the surface. During the uplift process, minerals cool and crystallize. This is what the process of formation of igneous rocks looks like.

Depending on the depth at which solidification occurs, rocks are divided into several groups; a table of varieties may look like this:

Igneous rocks differ from clastic rocks in that they do not contain the remains of dead organisms. is one of the most famous among this group. Its composition includes: quartz and mica.

When a volcano erupts, magma reaches the surface of the earth, gradually cools and forms volcanic rocks. They do not contain large crystals, since the temperature drop occurs quite quickly. Representatives of such rocks are basalt and granite. They were often used in ancient times to make monuments and sculptures.

Volcanic clastic rocks

During the process of volcanic eruptions, not only the rock granite is formed, but also many others. In addition to the outpouring of lava, a large amount of debris flies into the atmosphere, which, together with clots of hardening lava, fall to the surface of the earth and form tephra. This pyroclastic material is gradually eroded, part of it is destroyed by water, and what remains is compacted and transformed into strong rocks - volcanic tuffs.

On the fault of these rocks one can see fragments, the spaces between which are filled with ash, sometimes clay or siliceous sedimentary substances.

Weathering of rocks

All rocks, while in nature, are exposed to many factors, resulting in weathering or destruction. Depending on the impact, there are several types of this process:

1. Physical weathering of rocks. Occurs due to temperature changes, as a result of which rocks crack; water enters these cracks, which can turn into ice at subzero temperatures. This is how the rock is gradually destroyed.
2. Chemical weathering is carried out under the influence of water, which enters the cracks of the rock and leaches and dissolves it. Marble, limestone, and salt are most susceptible to this effect.
3. Biological weathering occurs with the participation of living organisms. For example, plants destroy rock with their roots, and lichens that settle on them release some acids, which also have a destructive effect.

It is almost impossible to avoid the process of rock weathering.

Meaning of rocks

It is impossible to imagine a national economy without the use of rocks. This use began in ancient times, when man learned to process stones. Rocks are primarily used in the construction industry. Examples include the following:

• Marble.
• Limestone.
• Granite.
• Quartzite and others.

Their use in construction is based on strength and other important qualities.

Some rocks find their use in the metallurgical industry, for example, refractory clay, limestone, and dolomite. The chemical industry is inseparable from tripoli and diatomite.

Even light industry uses rocks for its needs. IN agriculture one cannot do without potassium salts and phosphorites, which are an important component of fertilizers.

Thus, we looked at rocks. And we can conclude that at present they are indisputable and necessary human assistants in almost every industry, starting with Everyday life and ending with construction. That is why the concept most often used is not a rock, but a mineral, which precisely expresses the significance of these natural deposits.

Sediments and sedimentary rocks formed during their diagenesis accumulate in relief depressions (at the bottom of oceans and seas, lakes, in rivers, intermountain depressions, etc.) and, as a rule, initially have a horizontal occurrence. The flattened geological bodies they form are called layers. Layer- this is a flattened geological body, relatively homogeneous in composition and structure, bounded by approximately parallel interfaces.

The upper boundary of the layer is called the roof, the lower - the sole.

Note. In addition to the term “layer”, the term “layer” is often used, which has a similar meaning, but is usually used for minerals, such as coal, limestone, etc.

The distance between the roof and the base of the layer determines the thickness of this layer. There are two types of power: true power- the shortest distance between the roof and the bottom of the formation (perpendicular) and apparent power- any other (not the shortest) distance between the sole and the roof.

The alternation of layers determines the layered structure of sedimentary rocks.

Groups of layers that have some common characteristics that distinguish them from adjacent layers (or groups of layers) are combined into packs. Such commonality may be associated with a structural feature (repeated interlayering of two or more varieties of rocks at a certain thickness of the section), differences in lithological composition (enrichment in mineral components, ferruginization, etc.) or other features that visually distinguish a group of layers from the total thickness of the sequence.

The shape of the layering reflects the nature of the movement of the medium in which sediment accumulation occurs. There are four main types of layering: parallel (horizontal), wavy, oblique, and lenticular.

Parallel bedding, where the bedding surfaces are parallel, indicates a relatively static environment in which the sediment accumulated. Such conditions occur in lakes or sea basins below the level of action of waves and currents.

Wavy lamination has wavy-curved bedding surfaces. It is formed during movements that periodically change in one direction, for example, during ebbs, tides, and coastal waves in shallow areas of the sea.

Lenticular layering is formed during the rapid and variable movement of water or air, for example in river flows or the tidal strip of the sea. It is characterized by a variety of shapes and variability in the thickness of individual layers. Often the layer wedges out, which leads to its separation into separate parts or lenses. Genetically closely related to the wavy one.

Cross bedding refers to bedding with straight and curved bedding surfaces and with varying angles of fine bedding within the layer. It is formed when a medium moves in one direction, for example a river, stream, sea ​​current or air movement. In river flows, cross-bedding has a general slope in the direction of water movement. The deltaic variety of cross-bedding is larger and is characterized by a smooth attachment of the cross-layers to the base of the layer, while at the top the cross-layers disappear and coarser material appears. Cross-bedding of marine sediments is also characterized by larger sizes and a relatively small slope. In shallow waters, very thin, interlocking cross-bedding forms, oriented in different directions.

Types of layering (layer frequency)

I - wavy (and lenticular), II - horizontal, III - oblique

The structural features of the layering surfaces help to clarify the origin and conditions of occurrence of sedimentary strata. Such features include: fossil ripple marks, primary desiccation cracks, traces of the vital activity of organisms, imprints of raindrops, ice crystals, etc.

Primary and disturbed occurrence of layers

Most precipitation occurs in marine or continental bodies of water or on coastal plains. The occurrence of sediments is practically horizontal (the angle of inclination is no more than 1 o). This occurrence is called primary. Primary occurrence with a steeper rock formation, reaching 3-4 o, and sometimes 10 o, can occur on the slopes of ground and underwater hills, canyons, and ledges. The primary occurrence of sedimentary rocks is preserved relatively rarely and is disturbed by subsequent tectonic movements, which leads to their inclined occurrence, the formation of folded and faulty faults.

Layers of sedimentary rocks can have conformable and unconformable occurrence in relation to each other. When consonant occurrence, each overlying layer, without any traces of a break in the accumulation of sediments, overlies the underlying rocks. Dissent bedding occurs when there is a break in sedimentation between the overlying and underlying layers and the stratigraphic sequence is disrupted. Unconformity may be parallel when the layers, despite a break in sedimentation, remain parallel and corner, when one thickness lies with a break in relation to another at a certain angle. For example, when a layer of sandstone lies horizontally on a folded limestone layer. Identification of stratigraphic unconformities is one of the most important tasks of geological mapping and is carried out using the following features:

1. the characteristic structure of the unconformity surface, which has irregularities, hollows, and ledges;
2. angular unconformity between layers of different ages;
3. a sharp age gap between the fauna in the above and underlying layers;
4. a sharp difference in the degree of metamorphism of the two adjacent layers;
5. the presence of a basal conglomerate at the base of an unconformably overlying series of rocks;
6. a sharp transition from marine to continental sediments and vice versa;
7. traces of weathering on the surface of the unconformity.

Plicative dislocations of rock layers

As a result of the action of plastic deformations of rocks, a disturbed occurrence of layers of the earth's crust occurs without a visible break in their continuity. These types of faults are called plicative dislocations. These include the formation of monoclines, folds and flexures.

Monoclinal occurrence is formed when horizontally lying rocks, as a result of tectonic movements, acquire a slope at one angle over a significant area. Monocline is the simplest form of plicative dislocations, widely manifested in the covers of young and ancient platforms. There are slightly inclined (up to 15 o), flat (16-30 o), steep (30-75 o), and upright (80-90 o) monoclines.

Folded deformations or folds- these are wavy bends of layers without breaking the continuity of rocks. This type of dislocation is most widely manifested. In all types of folds, several basic elements are distinguished.

The part of the fold where the layers bend is called castle, vault or core. Wings- lateral parts of the folds adjacent to the arch. Fold angle- the angle formed by lines that are a continuation of the wings of the fold. Axial surface of the fold- an imaginary plane passing through the inflection points of the layers and dividing the corner of the fold in half. Centerline (fold axis)- the line of intersection of the axial surface with a horizontal plane or with a relief surface. The axial line characterizes the orientation of the fold in plan and is determined by the azimuth of the strike. Fold hinge- the line of intersection of the axial surface of the fold with the surface of one of the layers that make up the fold. It characterizes the structure of the fold along the axial surface (vertically) and is determined by the azimuth and angle of subsidence or uplift. The dimensions of the folds are characterized by length, width, height. Fold length- this is the distance along the center line between adjacent bends of the hinge. Fold width- the distance between the center lines of two adjacent anticlines or synclines. Height fold is the vertical distance between the lock of an anticline and the lock of an adjacent syncline.

Folds whose layers are bent upward are called anticlines. In these folds, more ancient rocks are exposed in the core on the day surface, and younger rocks are exposed on the wings and they are inclined from the core. Folds whose layers are bent downwards are called synclines. They have younger rocks exposed in their core, and their wings are tilted towards the core. These are the two main forms of folds.

Depending on the position of the axial surface in space, the following types of folds are distinguished.

Straight folds- the axial surface is vertical, and the wings fall into different sides at the same angles.

Sloping folds- the axial surface is inclined to the horizon, and the wings fall in different directions at different angles.

Overturned folds- the axial surface is steeply inclined, and the wings fall (tilted) to one side at different angles. In these folds, normal and inverted wings are distinguished.

Lying folds- the axial surface is parallel to the horizontal surface. The wings are tilted to one side at one angle.

Classification of folds according to the position of the axial plane

The shape of the folds also depends on the relationship between the wings and the lock. Depending on this, the folds may be sharp, when the wings form an acute angle (up to 90 o), stupid, with an angle of more than 90 o, isoclinal, with parallel wings and a blunt lock, fan-shaped, with pinched wings, chest with a flat wide lock.

In the longitudinal section there are folds linear, in which the length exceeds the width by more than three times, brachyform, with a length to width ratio of less than three and dome-shaped, with approximately the same dimensions of the length and width of the fold.

The fold hinge along strike often experiences subsidence or uplift and is not a straight line, but a wavy line. This phenomenon is called undulation. In this case, the closure of the fold is observed, when one wing along the axis gradually passes into the other. In anticlinal folds such closure is called periclinal, and in synclinal ones - centriclinal.

Varieties of anticlinal folds are diapiric folds And salt domes. Their formation is associated with the presence in the cores of these folds of plastic rocks (clays, salts, gypsum), which, under the influence of enormous pressure from the overlying rocks, are squeezed out and embedded in these rocks, forming a gentle arch and steep side surfaces.

The most widely developed types of diapiric folds are salt domes and clay diapirs. Salt domes have a core composed of plastic rocks and more fragile host rocks. The core bears the characteristics of active piercing, and the host rocks passively adapt to the movement of the core. Very often the salt in the core is shaped like a cylindrical column, forming a “salt rod”. When salt masses are introduced, the dome arch is subjected to tension and numerous cracks and fractures can occur in it. Salt domes are often associated with industrial oil and gas accumulations. The formation of diapiric folds, according to Yu.A. Kosygin, as well as American researchers Barton, Nelton and others, occurs only where the thickness of plastic rocks is at least 120 m, and their depth exceeds 300 m. Plastic rocks, being involved in a process of compression, in place with the surrounding brittle rocks, they are squeezed out of the wings into the cores of anticlines. Under favorable conditions, they can break through the overlying rocks and form diapiric folds.

(according to Benz)

Folds are often collected in groups and form parallel, echelon-shaped, bead-shaped, fascicle-shaped communities. Complex linear-folded structures form synclinoria and anticlinoria. Anticlinoria- These are large, complex anticlinal structures, hundreds and even thousands of kilometers long. They include many smaller anticlinal and synclinal folds. An example is the meganticlinorium Greater Caucasus. Synclinoria– these are the same large, complex structures, but generally synclinal structures, complicated by synclinal and anticlinal folds of lower orders. The combination of anticlinoria and synclinorium forms mountain ranges and mountain systems, such as the Alps, Caucasus, Tien Shan, etc.

A type of large folds are flexures, which are knee-shaped or stepped bends of layers or layers. In the area of ​​inflection, the thickness of the layers composing the flexure decreases somewhat and ruptures often occur. The parts of the flexure located on both sides of the bend are called wings. The closing wing remains in place and the lower wing, the lowered wing, stands out. The vertical amplitude of the displacement can be tens and even hundreds of meters. Flexures usually limit large platform structures, such as syneclises, marginal troughs, etc.

Faults (disjunctive dislocations)

Tectonic movements sometimes lead to a break in the continuity of rock layers and the formation of faults or disjunctive dislocations. A distinction is made between violations without significant displacement and violations with displacements. Disturbances without displacement are cracks. They vary in width (from millimeters to several meters), in length (from a few centimeters to tens of kilometers), in depth, shape (straight, arc-shaped, etc.), etc. In addition to cracks of tectonic origin, there are cracks of exogenous (non-tectonic) origin - drying cracks, landslides, collapses, rock expansion, spalling, etc.

Disjunctive violation; a-b - vertical displacement

Displacement faults include normal faults, reverse faults, strike-slip faults and thrust faults. The elements of tectonic faults are: the fault plane, the wings, the angle of inclination of the fault plane, the amplitude of the displacement.

Displacer– this is the plane along which the displacement occurs. The tilt angle of the shifter can vary from several degrees to 80-90 o. Wings– rock strata located on both sides of the fault plane. When the displacer is in an inclined position, the wing that is located above it is called a hanging wing, and the one located below it is called a recumbent wing. Offset amplitude– the magnitude of the relative movement of layers. There are displacement amplitudes along the fault plane, vertical, horizontal, and stratigraphic.

One of the most characteristic forms of discontinuous faults is reset. This is a violation in which the displacement is tilted towards the lowered wing (regardless of whether it is hanging or recumbent). If the displacement is inclined towards the uplifted rocks and goes under them, then such a violation is called uplift. In contrast to the types of violations described shift called a discontinuous fault in which movement occurs predominantly in the horizontal direction, and the displacement is located vertically. Often (or almost always) normal faults and strike-slip faults occur together and are called strike-slip faults and strike-slip faults.

Thrust called a dislocation with a rupture of layers and the pushing of one wing onto another along a relatively flat or horizontal plane. This is a reverse fault type fault, usually occurring together with folding. There are steep (more than 45 o), gentle (less than 45 o) and horizontal thrusts. These structures are widely manifested in folded areas. A thrust with large horizontal displacement is called carnage, whose hanging wing can move many kilometers and even tens of kilometers.

Fault disturbances often manifest themselves in the form of fault and reverse fault systems. In this case, peculiar structures are formed.

Graben– a lowered section of the earth’s crust limited by parallel faults of considerable extent.
Horst- an elevated section of the earth's crust contained between parallel faults.

Several parallel stepwise grabens form a complex graben. This applies to the structures of the Great African Lakes (Tanganyika, Alberta, Rudolph), the Red Sea Rift, the Lake Baikal Rift, the Rhine Graben, etc.

The largest thrusts and uplifts, characterized by rock movements of tens of kilometers along flat, horizontal and wavy surfaces, are called covers. Displaced masses of the hanging wing, called allochthon, and the recumbent wing remaining in place, called autochthonous. Integuments develop in areas with a complex integumentary fold structure. They are widespread in the Alps, Apennines, Himalayas, Carpathians, central and southeastern Caucasus, on the western slopes of the Urals, Verkhoyansk, Altai and other regions.

Sedimentary rocks occupy an impressive area globe. These include most of all the minerals that our planet is so rich in. Most sedimentary rocks are located on the mainland, continental slope and shelf, and only a small part is located on the bottom of seas and oceans.

Origin of sedimentary rocks

Under the destructive influence of sunlight, temperature fluctuations, and water, solid igneous rocks are weathered. They form fragments of various sizes, which gradually disintegrate into the smallest particles.

Wind and water transport these particles, which at some stage begin to settle, thereby forming loose accumulations on the land surface and at the bottom of water bodies. Over time, they harden, become denser, and acquire their own structure. This is how sedimentary rocks are formed.

Rice. 1. Sedimentary rocks

Like metamorphic rocks, sedimentary rocks are classified as secondary rocks. They lie only on the surface of the earth's crust, occupying about 3/4 of the area of ​​the entire planet.

Since almost all construction work is carried out on sedimentary rocks, it is very important to perfectly know the properties, composition and “behavior” of this type of rock. The science of engineering geology deals with these and many other issues.

The main feature of sedimentary rocks is layering, unique to each natural compound. As a result of shifts in the earth's crust, the original forms of occurrence of sedimentary rocks are disrupted: all kinds of breaks, cracks, faults, and folds appear.

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Rice. 2. Layering of sedimentary rocks

Rock classification

The deposition process can take place different ways. Depending on its specificity, several main groups of sedimentary rocks are distinguished:

• clastic - formed under the influence of weathering and further transfer of igneous rock particles;
• chemogenic - the result of the isolation and precipitation of substances that are formed from saturated aqueous solutions;
• biochemical - are formed as a result of chemical reactions with the participation of living organisms;
• biogenic - the result of decomposition of the remains of plant and animal organisms.

In nature, mixed groups of sedimentary rocks are often found, the formation of which was influenced by several factors. Yes, one of bright examples mixed-type sedimentary rocks are limestone, which can equally be of chemogenic, organogenic, biochemical or clastic origin.

Rice. 3. Limestone

What have we learned?

Sedimentary rocks occupy vast areas of the Earth's surface. They can be located both on land and at the bottom of seas and oceans. Any sedimentary rock is formed from destroyed and modified igneous rocks. The classification of rocks is based on the characteristics of the sedimentation process, which can occur under the influence of many factors.